Osteoderm morphology in recent and fossil euphractine xenarthrans

The presence of osteoderms within the integument, forming a carapace, is one of the most distinctive features of armadillos with the external morphology of these elements forming the basis of most systematic schemes. This is especially true for fossil taxa, where these elements are most frequent in the palaeontological record. A detailed study of osteoderms from the cephalic shield and different regions of the dorsal armour of Chaetophractus villosus (Euphractinae, Xenarthra) was made and compared to those of the extant genus Dasypus (Dasypodinae, Xenarthra), and the extinct genus ?Eutatus. Three distinct histological zones were recognized: outer and inner zones are thin, formed by regular compact bone, the middle zone is thicker, with large cavities that contain mainly adipose tissue, hair follicles, and sweat and sebaceous glands. The internal structure of ?Eutatus (also a member of Euphractinae) osteoderms is close to that of C. villosus, consistent with the notion that these taxa are phylogenetically closely related. In contrast, Dasypus shows marked differences. Dasypus shows hair follicles associated with both gland types (sweat and sebaceous) and connected to foramina on the external surface. Although not observed in adult C. villosus, it has been documented during embryonic development, only to atrophy later in ontogeny. Furthermore, the presence of red bone marrow is rare in C. villosus, but widespread in Dasypus novemcinctus osteoderms. These results suggest an early split of both subfamilies and support the hypothesis that the Euphractinae are more derived than the Dasypodinae.     

Radiographic estimation of long bone cross-sectional geometric properties

Because of their biomechanical significance, cross-sectional geometric properties of long bone diaphyses (areas, second moments of area) have been increasingly used in a number of form/function studies, e.g., to reconstruct body mass or locomotor mode in fossil primates or to elucidate allometric scaling relationships among extant taxa. In the present study, we test whether these biomechanical section properties can be adequately estimated using biplanar radiographs, as compared to calculations of the same properties from computer digitization of cross-sectional images. We are particularly interested in smaller animals, since the limb bone cortices of these animals may not be resolvable using other alternative noninvasive techniques (computed tomography). The test sample includes limb bones of small (25–5,000 g) relatively generalized quadrupedal mammals—mice, six species of squirrels, and Macaca fascicularis. Results indicate that biplanar radiographs are reasonable substitutes for digitized cross-sectional images for deriving areas and second moments of area of midshaft femora and humeri of mammals in this size range. Potential application to a variety of questions relating to mechanical loading patterns in such animals is diverse. © 1993 Wiley-Liss, Inc.     

Is Palaeospondylus gunni a fossil larval lungfish? Insights from Neoceratodus forsteri development

The enigmatic Devonian fossil Palaeospondylus gunni was identified as a larval form, metamorphosing into the lungfish Dipterus valenciennesi. Morphological features used to identify P. gunni as a larval lungfish include enlarged cranial ribs, rudimentary limb girdles, and absence of teeth. However, this combination of features does not characterize the extant lungfish Neoceratodus forsteri, even at very young stages, nor early stages of Devonian and younger fossil lungfish. Absence of teeth is problematic because early ontogenetic stages of fossil and living lungfish possess full dentitions including marginal teeth. Also problematic are cranial ribs as a defining character of lungfish, as these also occur in certain actinopterygians.It is argued that Neoceratodus is an obligate neotene (reproductively mature larva), with the implication that metamorphosis was a feature of the ontogeny of early lungfish. Pedomorphic characters have been recognized in Neoceratodus and other post-Devonian lungfish, including large cells and correspondingly large genome size; these latter characters correlate with neoteny in salamanders. Small cells preserved in fossil bone suggest that Devonian lungfish had a smaller genome than post-Devonian lungfish, implying that they were not neotenic. As fossil lungfish cell sizes (and genomes) increased in the late Paleozoic, the diversity of lungfish morphologies decreased, so that taxa like Sagenodus and Conchopoma show morphological similarity to Neoceratodus, marking a point in phylogeny at which metamorphosis was potentially lost. Since ancestral larval characters are retained in neotenic adults, we predict that Devonian larvae should resemble these post-Devonian taxa, a prediction which Palaeospondylus does not fulfill.     

Functional and historical determinants of shape in the scapula of Xenarthran mammals: Evolution of a complex morphological structure

The mammalian scapula is a complex morphological structure, composed of two ossification plates that fuse into a single structure. Most studies on morphological differentiation in the scapula have considered it to be a simple, spatially integrated structure, primarily influenced by the important locomotor function presented by this element. We used recently developed geometric morphometric techniques to test and quantify functional and phylogenetic influences on scapular shape variation in fossil and extant xenarthran mammals. The order Xenarthra is well represented in the fossil record and presents a stable phylogenetic hypothesis for its genealogical history. In addition, its species present a large variety of locomotor habits. Our results show that approximately half of the shape variation in the scapula is due to phylogenetic heritage. This is contrary to the view that the scapula is influenced only by functional demands. There are large‐scale shape transformations that provide biomechanical adaptation for the several habits (arboreality, terrestriality, and digging), and small scale‐shape transformations (mostly related to the coracoid process) that are not influenced by function. A nonlinear relationship between morphometric and phylogenetic distances indicates the presence of a complex mixture of evolutionary processes acting on shape differentiation of the scapula. J. Morphol. 241:251–263, 1999. © 1999 Wiley‐Liss, Inc.     

Early hominin limb proportions

Recent analyses and new fossil discoveries suggest that the evolution of hominin limb length proportions is complex, with evolutionary reversals and a decoupling of proportions within and between limbs. This study takes into account intraspecific variation to test whether or not the limb proportions of four early hominin associated skeletons (AL 288-1, OH 62, BOU-VP-12/1, and KNM-WT 15000) can be considered to be significantly different from one another. Exact randomization methods were used to compare the differences between pairs of fossil skeletons to the differences observed between all possible pairs of individuals within large samples of Gorilla gorilla, Pan troglodytes, Pongo pygmaeus, and Homo sapiens. Although the difference in humerofemoral proportions between OH 62 and AL 288-1 does not exceed variation in the extant samples, it is rare. When humerofemoral midshaft circumferences are compared, the difference between OH 62 and AL 288-1 is fairly common in extant species. This, in combination with error associated with the limb lengths estimates, suggests that it may be premature to consider H. (or Australopithecus) habilis as having more apelike limb proportions than those in A. afarensis. The humerofemoral index of BOU-VP-12/1 differs significantly from both OH 62 and AL 288-1, but not from KNM-WT 15000. Published length estimates, if correct, suggest that the relative forearm length of BOU-VP-12/1 is unique among hominins, exceeding those of the African apes and resembling the proportions in Pongo.Evidence that A. afarensis exhibited a less apelike upper:lower limb design than A. africanus (and possibly H. habilis) suggests that, if A. afarensis is broadly ancestral to A. africanus, the latter did not simply inherit primitive morphology associated with arboreality, but is derived in this regard. The fact that the limb proportions of OH 62 (and possibly KNM-ER 3735) are no more human like than those of AL 288-1 underscores the primitive body design of H. habilis.     

Proportions and function of the limbs of glyptodonts

Vizcaíno, S.F., Blanco, R.E., Bender, J.B. & Milne, N. 2010: Proportions and function of the limbs of glyptodonts. Lethaia, Vol. 44, pp. 93–101. This study examines the limb bone proportions and strength of glyptodonts (Xenarthra, Cingulata). Two methods are used to estimate the body mass and location of the centre of gravity of the articulated specimens. These estimates, together with measurements of the femur and humerus, are used to calculate strength indicators (SI). The other long bones of the limbs are used to calculate limb proportion indices that give an indication of digging ability, speed, and limb dominance in armadillos, the glyptodonts’ living closest relatives. The results show that regardless of how the body mass and centre of gravity are calculated, the majority of the glyptodont’s weight is borne by the hindlimbs. The SI calculations show that femora are sturdy enough to bear these loads. The fact that the femora have higher SI than the humerii indicates that sometimes the hindlimbs are required to bear an even greater proportion of the body weight, possibly when rising to a bipedal posture or pivoting on their hindlimbs to deliver a blow with their armoured tail. The analysis of limb proportions indicates that both the hindlimb and the forelimb have proportions that correlate strongly with body mass. This outcome supports the other results, but also shows that forelimbs must be also involved in manoeuvring the glyptodont body. □Glyptodonts, Mammalia, Xenarthra, limbs, strength indicators.     

主成分分析法在壳斗科植物化石鉴定中的应用*

壳斗科化石是北半球新生代地层的优势分子,然而由于其属种众多,叶片属种间特异性不明显,该科叶片化石的鉴定是古植物学研究的难点之一。面对化石标本不完整的性状特征信息,如何剔除冗余特征,重点考虑具有鉴定意义的标本特征,就显得非常必要。本研究通过调研多种降维算法,考虑到植物特征编码及赋值的数值特性,选用主成分分析法,以壳斗科青冈亚属植物叶片为例,对可能在化石叶片上观察到的22个性状特征(变量)进行降维处理,挑选出对于壳斗科化石叶片分类鉴定起主要作用的10个性状特征,并将其应用于化石鉴定进行验证。结果表明,仅考虑经过主成分分析法压缩挑选的10个主要性状特征,仍然能够实现壳斗科化石植物的准确鉴定。主成分分析法应用于壳斗科性状特征的降维处理效果良好,剔除冗余特征对标本鉴定结果没有影响。     

Does skeletal anatomy reflect adaptation to locomotor patterns? cortical and trabecular architecture in human and nonhuman anthropoids

Although the correspondence between habitual activity and diaphyseal cortical bone morphology has been demonstrated for the fore- and hind-limb long bones of primates, the relationship between trabecular bone architecture and locomotor behavior is less certain. If sub-articular trabecular and diaphyseal cortical bone morphology reflects locomotor patterns, this correspondence would be a valuable tool with which to interpret morphological variation in the skeletal and fossil record. To assess this relationship, high-resolution computed tomography images from both the humeral and femoral head and midshaft of 112 individuals from eight anthropoid genera (Alouatta, Homo, Macaca, Pan, Papio, Pongo, Trachypithecus, and Symphalangus) were analyzed. Within-bone (sub-articular trabeculae vs. mid-diaphysis), between-bone (forelimb vs. hind limb), and among-taxa relative distributions (femoral:humeral) were compared. Three conclusions are evident: (1) Correlations exists between humeral head sub-articular trabecular bone architecture and mid-humerus diaphyseal bone properties; this was not the case in the femur. (2) In contrast to comparisons of inter-limb diaphyseal bone robusticity, among all species femoral head trabecular bone architecture is significantly more substantial (i.e., higher values for mechanically relevant trabecular bone architectural features) than humeral head trabecular bone architecture. (3) Interspecific comparisons of femoral morphology relative to humeral morphology reveal an osteological "locomotor signal" indicative of differential use of the forelimb and hind limb within mid-diaphysis cortical bone geometry, but not within sub-articular trabecular bone architecture.     

Molecular Decay of the Tooth Gene Enamelin (ENAM) Mirrors the Loss of Enamel in the Fossil Record of Placental Mammals

Vestigial structures occur at both the anatomical and molecular levels, but studies documenting the co-occurrence of morphological degeneration in the fossil record and molecular decay in the genome are rare. Here, we use morphology, the fossil record, and phylogenetics to predict the occurrence of “molecular fossils” of the enamelin (ENAM) gene in four different orders of placental mammals (Tubulidentata, Pholidota, Cetacea, Xenarthra) with toothless and/or enamelless taxa. Our results support the “molecular fossil” hypothesis and demonstrate the occurrence of frameshift mutations and/or stop codons in all toothless and enamelless taxa. We then use a novel method based on selection intensity estimates for codons (ω) to calculate the timing of iterated enamel loss in the fossil record of aardvarks and pangolins, and further show that the molecular evolutionary history of ENAM predicts the occurrence of enamel in basal representatives of Xenarthra (sloths, anteaters, armadillos) even though frameshift mutations are ubiquitous in ENAM sequences of living xenarthrans. The molecular decay of ENAM parallels the morphological degeneration of enamel in the fossil record of placental mammals and provides manifest evidence for the predictive power of Darwin''s theory.     

Brief Communication: Calculating hominin and nonhuman anthropoid femoral head diameter from acetabular size

Femoral head size provides important information on body size in extinct species. Although it is well‐known that femoral head size is correlated with acetabular size, the precision with which femoral head size can be estimated from acetabular size has not been quantified. The availability of accurate 3D surface models of fossil acetabular remains opens the possibility of obtaining accurate estimates of femoral head size from even fragmentary fossil remains [Hammond et al.,: Am J Phys Anthropol 150 (2013) 565–578]. Here we evaluate the relationship between spheres fit to surface models of the femoral head and acetabulum of a large sample of extant anthropoid primates. Sphere diameters are tightly correlated and scale isometrically. In spite of significant taxonomic and possibly functional differences in the relationship between femoral head size and acetabulum size, percent prediction errors of estimated femoral head size remain low regardless of the taxonomic composition of the reference sample. We provide estimates of femoral head size for a series of fossil hominins and monkeys. Am J Phys Anthropol 155:469–475, 2014. © 2014 Wiley Periodicals, Inc.     

Body mass estimation in xenarthra: A predictive equation suitable for all quadrupedal terrestrial placentals?

The Magnorder Xenarthra includes strange extinct groups, like glyptodonts, similar to large armadillos, and ground sloths, terrestrial relatives of the extant tree sloths. They have created considerable paleobiological interest in the last decades; however, the ecology of most of these species is still controversial or unknown. The body mass estimation of extinct species has great importance for paleobiological reconstructions. The commonest way to estimate body mass from fossils is through linear regression. However, if the studied species does not have similar extant relatives, the allometric pattern described by the regression could differ from those shown by the extinct group. That is the case for glyptodonts and ground sloths. Thus, stepwise multiple regression were developed including extant xenarthrans (their taxonomic relatives) and ungulates (their size and ecological relatives). Cases were weighted to maximize the taxonomic evenness. Twenty‐eight equations were obtained. The distribution of the percent of prediction error (%PE) was analyzed between taxonomic groups (Perissodactyla, Artiodactyla, and Xenarthra) and size groups (0–20 kg, 20–300 kg, and more than 300 kg). To assess the predictive power of the functions, equations were applied to species not included in the regression development [test set cross validation, (TSCV)]. Only five equations had a homogeneous %PE between the aforementioned groups. These were applied to five extinct species. A mean body mass of 80 kg was estimated for Propalaehoplophorus australis (Cingulata: Glyptodontidae), 594 kg for Scelidotherium leptocephalum (Phyllophaga: Mylodontidae), and 3,550.7 kg for Lestodon armatus (Phyllophaga: Mylodontidae). The high scatter of the body mass estimations obtained for Catonyx tarijensis (Phyllophaga: Mylodontidae) and Thalassocnus natans (Phyllophaga: Megatheriidae), probably due to different specializations, prevented us from predicting its body mass. Surprisingly, although obtained from ungulates and xenarthrans, these five selected equations were also able to predict the body mass of species from groups as different as rodents, carnivores, hyracoideans, or tubulidentates. This result suggests the presence of a complex common allometric pattern for all quadrupedal placentals. J. Morphol., 2008. © 2008 Wiley‐Liss, Inc.     

The evolution of encephalization in caniform carnivorans

A weighted-average model, which reliably estimates endocranial volume from three external measurements of the neurocranium of extant taxa in the mammalian order Carnivora, was tested for its applicability to fossil taxa by comparing model-estimated endocranial volumes to known endocast volumes. The model accurately reproduces endocast volumes for a wide array of fossil taxa across the crown radiation of the Carnivora, three stem carnivoramorphan taxa, and Pleistocene fossils of two extant species. Applying this model to fossil taxa without known endocast volumes expanded the sample of fossil taxa with estimated brain volumes in the carnivoran suborder Caniformia from 11 to 60 taxa. This then allowed a comprehensive assessment of the evolution of relative brain size across this clade. An allometry of brain volume to body mass was calculated on phylogenetically independent contrasts for the set of extant taxa, and from this, log-transformed encephalization quotients (logEQs) were calculated for all taxa, extant, and fossil. A series of Mann-Whitney tests demonstrated that the distributions of logEQs for taxa early in caniform evolutionary history possessed significantly lower median logEQs than extant taxa. Median logEQ showed a pronounced shift around the Miocene-Pliocene transition. Support tests, based on likelihood ratios, demonstrated that the variances of these distributions also were significantly lower than among modern taxa, but logEQ variance increased gradually through the history of the clade, not abruptly. Reconstructions of ancestral logEQs using weighted squared-change parsimony demonstrate that increased encephalization is observed across all major caniform clades (with the possible exception of skunks) and that these increases were achieved in parallel, although an "ancestor-descendant differencing" method could not rule out drift as a hypothesis. Peculiarities in the estimated logEQs for the extinct caniform family Amphicyonidae were also investigated; these unusual patterns are likely due to a unique allometry in scaling brain to body size in this single clade.     

What is a cursorial mammal?

This paper focuses on the concept of cursoriality in mammals and aims to point out the confusion that can arise when a classical term is not explicitly redefined or expanded to incorporate the results of biomechanical techniques. Historically, the definition of 'cursorial' was based qualitatively on an animal's morphology and behaviour, generally referring to large, terrestrial mammals that ran fast or far across open spaces. However, in recent years, as biomechanicists have learned how to quantify aspects of limb movement and bone orientation, a more specific meaning of this term has come into use. Results from these new techniques have highlighted the lack of specificity in the historical definition and have led us to propose a clarified, quantitative definition of 'cursorial'. The exceptional nature of bovids and primates with respect to this new definition is also addressed in our analysis. We recognize that the definition we propose is, itself, not sufficient because it cannot be applied to fossil taxa and because kinematic data are still lacking for many taxa. Hence, we look forward to the eventual adoption of an even more expanded definition or suite of terms that will further distinguish between all attributes of cursorial mammals and that will reflect an increased understanding of their evolutionary origins.     

A fossil heron from the early Oligocene of Belgium: the earliest temporally well‐constrained record of the Ardeidae

We describe the earliest temporally well‐constrained fossil that can be assigned to the Ardeidae (herons), from the lowermost Oligocene (32.0–33.0 million years ago) of Belgium. The specimen, a partial tarsometatarsus, belongs to a small species and is described as Proardea? deschutteri n. sp. It exhibits the characteristic tarsometatarsus morphology found in extant heron species, but a confident assignment to one of the ardeid subclades is not possible and even the assignment of the new fossil species to the crown group (the clade including the extant species) cannot be established. The fossil indicates a divergence of herons from their sister taxon by at least the earliest Oligocene, and current paleontological data suggest that herons arrived in Europe shortly after a major faunal turnover at the Eocene/Oligocene boundary. We consider that dispersal is the likely reason for the sudden appearance of herons in the earliest Oligocene of Europe but it is uncertain from where exactly this took place, with Asia and Africa being among the candidate areas.     

Mandibular shape correlates of tooth fracture in extant Carnivora: implications to inferring feeding behaviour of Pleistocene predators

Percentages of tooth fracture and mandible shape are robust predictors of feeding habits in Carnivora. If these parameters co‐vary above the species level, more robust palaeobiological inferences could be made on fossil species. A test of association is presented between mandible shape and tooth fracture in a subset of extant carnivorans together with large Pleistocene fossil predators from Rancho La Brea (Canis dirus, Panthera atrox, and Smilodon fatalis). Partial least square (PLS) and comparative methods are employed to validate co‐variation of these two parameters in extant carnivorans. Association between mandible shape and percentage of tooth fracture is strongly supported, even if both blocks of data exhibit a phylogenetic signal to a different degree. Dietary adaptations drive shape/fracture co‐variation in extant species, although no significant differences occur in the PLS scores between carnivores and bone/hard food consumers. The fossil species project into PLS morphospace as outliers. Their position suggests a unique feeding behaviour. The increase in the size of prey, together with consumption of skin and hair from carcasses in a cold environment, might have generated unusual tooth breakage patterns in large predators from Rancho La Brea. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 106 , 70–80.     

The functional morphology of weight bearing: limb joint surface area allometry in anthropoid primates

Biomechanical scaling of long bone joint surface areas was investigated in 13 species of anthropoid primates. It was proposed that joint surface areas should scale with positive allometry with respect to body size in order to maintain relatively constant safety factors for joints in small and large animals and that modifications from the overall pattern of scaling may be expected in the limb joints of species exhibiting specialized locomotor behaviours that radically alter limb loading. Within anthropoids, the brachiating primates, white-handed gibbons ( Hylobates lar ) and black-handed spider monkeys ( Ateles geoffroyi ), were used to test this hypothesis. Total joint surface areas were found to scale with significant positive allometry in 11 of 12 limb joints. The observed pattern of interspecific allometry supports the hypothesis that weight bearing is a major constraint on the design of joints. This positive interspecific allometry is reflected at the intraspecific level as well, with larger joints of larger species showing significant intraspecific scaling. Suspensory species showed no significant deviations from the overall anthropoid pattern, despite their reduced compressive loading of the limb joints, even after controlling for joint mobility. These results suggest that, while evolutionary changes in locomotor behaviour that produce significant increases in loading of a joint may be accompanied by selection for increased joint surface areas, adoption of locomotor repertoires that reduce limb loading may have no selective effect on joint morphology, and joint design in these cases will reflect the biomechanics of the ancestral locomotor condition.     

An Overview of the Presence of Osteoderms in Sloths: Implications for Osteoderms as a Plesiomorphic Character of the Xenarthra

The presence of osteoderms in the skin of some extinct sloths and in cingulates (armadillos, pampatheres, and glyptodonts) has often been considered a pleisomorphic character of the Xenarthra. While osteoderms are known from the earliest cingulates, they are absent in most sloths including the two extant taxa and only appear late in their fossil record. Osteoderms are currently only reported from five genera of mylodonts and two megatheres, out of the over 100 currently recognized genera of sloths. Consequently, rather than a plesiomorphic character of the Xenarthra, which has been secondarily lost in sloths, it is more likely that osteoderms in sloths are the result of parallel evolution to the cingulates that independently evolved in one, possibly two different sloth clades.